How to mount a fan pipe: step-by-step instruction and analysis of common mistakes

Vasily Borutsky
Checked by a specialist: Vasily Borutsky
Author: Elena Nikolaeva
Last update: September 2019

Arrangement of ventilation of an independent or centralized drainage system is impossible without the installation of a special fan outlet. The element blocks the return flow of gases to the bathrooms, acting as a connecting component between the septic tank and the atmosphere.

The installation technology of the riser is quite simple. But before you begin to work, you need to understand the principle of the ventilation duct and understand how to install the fan pipe in the house. The answers to these questions are detailed in the article.

The principle of the fan pipe

The fan pipe is a structural element that connects the pipeline to a specially constructed ventilation duct. Its key purpose is to remove gases and odors from the sewage system.

Scheme of structural elements of the system
The presence of a ventilation riser in the system guarantees the absence of unpleasant loud noises in the living quarters that occur when the water is drained and “fragrances” of sewage sewage (+)

The length and shape of this element can be arbitrary. There are models of vertical and horizontal execution, beveled at a right or acute angle.

The principle of operation of a fan pipe is simple. Wastewater, falling into a vertical riser, creates a vacuum in the cavity of the pipeline. It can be partially compensated by water, which acts as a water damper in siphons of installed plumbing.

But if a vertically installed riser has a large length and at the same time at one moment there is a one-time powerful discharge of the spent liquid, then a vacuum appears in the sewer pipe.

Formed piston from the liquid with all its strength and a characteristic “smacking” sound at one moment breaks and breaks through the plumbing hydraulic damper, emptying the siphons.

As a result, water is completely sucked out of all hydraulic locks. Therefore, obstacles to sewer "aromas" does not remain. Due to this, they quickly spread throughout the building.

Pumps out the contents of the pit
This effect is also manifested when the fecal pump quickly pumps out the contents of the cesspool or septic tank into the tank of the sewer machine

The trouble is that things are not limited to the appearance of an unpleasant “fragrance” in living rooms. The natural process of decomposition of feces is accompanied by the release of gases harmful to households: methane and hydrogen sulfide.

If the system is equipped with a fan riser, there are no such consequences at the time of “stuffing”, since the vacuum created in the collector simply does not have time to break through the hydraulic valves in siphons.

This is prevented by the flow of atmospheric air, which, simultaneously with the occurrence of vacuum, is drawn into the system, blocking the penetration of gases into the room when the septic tank is drained and pumped out.

Conditions for installing a fan riser

According to the current building standards 2.04.01-85 *, and in particular the section “Internal water supply and sewerage of buildings”, such an element as a sewer pipe must be installed in the following cases:

  1. In one-story buildings, if they include pools and other structures that are capable of dispensing one-off portions of large volumes of wastewater.
  2. When arranging sewer risers collected from pipes with a diameter of 50 mm.
  3. In low-rise buildings, provided that each floor is equipped with a water supply and sewage system.

It is easiest to determine whether the installation of a fan riser is required for specific conditions, focusing on the maximum amount of a single portion of drains.

Condition for installation of the structure
Installation of a fan riser is necessary if the effluent stream is capable of completely blocking the flow of a vertically installed riser even for a short time period

In multi-storey buildings, where communications are installed on each floor and in each apartment, the installation of a fan riser is a rigorous condition. The riser in this case is displayed on the roof of the building.

Features of installation activities

The technology of the device of the fan riser is quite simple. Installation work can be performed even by a novice master.

Selection of required materials

The three key elements of the ventilation system are the fan pipe, valve and drainage trap. Equality of pressures in the system provides each of them.

Siphons with a water trap are installed at the stage of installation of intra-house sanitary fixtures.

The principle of formation of a water seal
Siphons operate on the principle of communicating vessels, in which at the time of discharge of fluid into the cavity of one vessel, the second overflows and drains water into the sewer

The fan riser is a continuation of the sewer pipeline. And for its arrangement, you can use the pipes used in the assembly of the main system.

For installation of the ventilation duct, it is best to choose plastic pipes. They do not freeze, are not exposed to the destructive effects of moisture and are resistant to corrosion.

Polymeric products during the arrangement of the sewer system are also advantageous in that, due to the smoothness of the walls, they do not produce noise when sewage flows through the pipeline.

Determining the size of the fan pipe, it is worth following the rule that the throughput of the 50th pipe is almost 16 times less than the 110th. Using D 50 mm pipes, you will not get an efficient ventilation system, but a useless set of connecting pipes.

Structural elements of the sewage system
To connect the fan pipe, polymer products with a diameter of 110 mm are most often chosen so that the cross-section of the elements coincides with the diameter of the constructed sewer riser

Regardless of the design and location, each fan pipe is equipped with a check valve. Indeed, even if the pipeline was originally laid correctly, then due to insufficiently reliable fixing of pipes on the walls and under the influence of the natural process of building shrinkage, its slope can change.

In the event of a malfunctioning ventilation, air will enter the sewer from the nearest plumbing fixture. Most often, it becomes that element of sanitary ware, in which the smallest water shutter.

Each valve is equipped with inlet and outlet nozzles. A balloon filled with air is located in the cavity of the device. At the time of creating a vacuum, he presses on the membrane, which completely covers the chamber. Due to this, gases simply cannot get into the cavity of the pipe.

One option check valve
The main purpose of the non-return valve is to correct the situation by blocking the flow of gases in the case when the collector was laid under the wrong slope

In addition to the main function, the check valve helps to solve two key tasks:

  • prevents the return of effluents to plumbing fixtures;
  • protects the system from ingress of large mechanical impurities and penetration through a system of rodents.

But in order for the air valve to cope with the task assigned to it, it must be placed only in those rooms where the temperature is constantly observed above zero.

General installation recommendations

The main rule in the arrangement of the system is that the starting point is placed in the heated part of the building, where at any time of the year the temperature is positive and the final temperature is in the cold.

This solution allows you to provide the necessary temperature difference, creating the conditions for uninterrupted removal of "aromas" outside the building.

The layout of the discharge section
The outer section of the outlet pipe must be located in a place where the emitted sewer odors can disperse unhindered in the air

The vertical riser should be led directly to the roof of the building. The attic is not suitable for these purposes, since the draft will be weak, and the attic will “stink”.

When installing a fan pipe, it is important to adhere to a number of basic principles:

  1. The output of a riser equipped with a fan pipe must be placed separately. According to paragraph 17.19 of building codes, it cannot be organized together with a stove chimney or ventilation system.
  2. When a structural element is brought out onto a pitched roof, it is placed at a height of 500 mm, positioning it as close to the ridge as possible. If the roof is flat and also not operational, then the height of the exhaust part should be 300 mm.
  3. The distance of the fan pipe installed above the roof in a horizontal plane relative to balconies and windows that open in the house should be about 4 meters.
  4. Do not place the exhaust pipe under the eaves. With this arrangement, traction is reduced.

In a situation, if the roof is actively operated and other objects are placed on it, then the height of the outlet of the riser should be at least 3 meters. Provided that the channel is equipped in a prefabricated ventilation shaft, it is placed withstanding a distance of 100 mm from the edge.

The need for a vacuum valve
If the ventilation riser is located far from the toilet, then it is recommended to additionally put a vacuum valve on the plumbing fixture itself

Within the same fan pipe several risers can be combined simultaneously. But, in any case, since with such an arrangement ventilation is not forced, but gravity, it is advisable to avoid turns and various kinds of narrowing of the pipeline. Their presence may create undesirable resistance to air flow.

If the exhaust part is slightly offset from the riser, structural elements can be connected corrugated plastic sleeve.

Scheme of methods for connecting risers
Two variants of the applied methods of connecting several risers into a common fan pipe: serial in the form of a loop and parallel in the form of two independent exhaust systems (+)

At rooftop equipped with a fan pipe riser, there is no need to erect auxiliary exhaust devices in the form of the same flyarka or deflector, as well as protective "mushrooms". This moment is clearly stated in paragraph 18.18 of the current SNiP.

The use of these devices can, on the contrary, give the opposite effect: the condensate formed upon lowering the ambient temperature will freeze and block the outlet openings. Installation vent deflector It will be advisable only in that situation if the building is located in an area with a warm climate.

How to connect a check valve

The fan pipe is connected to a pre-equipped ventilation duct. If the ventilation scheme assumes the presence of too few exhaust pipes, the fan pipe can also be separately removed through the nearest wall by placing the exhaust element horizontally in its upper part.

To do this, it is led through a wall opening, leading outside the building at a distance of 30-40 cm.

The ventilation valve is mounted in the free end of the pipe or bell. The main thing is that the pipe section on which the valve will be installed is located above the highest point of drainage from plumbing equipment.

Valve placement in the pipe
The check valve can be mounted in two ways, placing it inside the fan pipe and installing it outside, positioning both in horizontal and vertical planes

With the internal placement of the element, it is necessary to clean the pipe section where the valve will be installed and treat it with a degreasing compound.

A special insert is buried inside the pipe, which can be purchased at any hardware store. The valve is buried in the insert, placing it in the opposite direction of the movement of effluents. It is positioned so that the petals of the device are unbent towards the plumbing.

Detailed technology for installing a non-return valve for sewage is described in this article.

When installing a fan pipe having a section of 110 mm, the check valve is connected using an adapter.

One way to install a check valve
One of the ways to install a check valve in the cavity of the fan pipe with its subsequent connection to the sewer system

An important point: all installation operations of the fan pipe should be carried out on dry surfaces. At the stage of fixing the check valve, do not use silicone sealants and any kind of lubricant.

Typical installation errors

Most often, the situation with the formation of vacuum in the system occurs when pipes of different diameters are used for its arrangement. For example: the toilet is connected to a pipe D 110 mm, the bath to the pipe D 50 mm, and the hole of the drain tank - D 70 mm.

Unpleasant stench in the bathrooms often appear when plumbing fixtures are equipped with siphons with insufficient volume. This is due to the fact that during irregular use of the devices in the siphons, the remaining water dries up, removing the water damper and opening up free access to the spread of “aromas”.

When choosing a place for placing a ventilation fan pipe, many make a mistake by placing it under the roof overhang.This leads to the fact that in winter, sliding and falling from the roof of the snow damages the outlet structure.

So that the condensate formed inside the ventilation duct does not freeze at subzero temperatures, the structure must be insulated.

Conclusions and useful video on the topic

How to design and arrange a fan pipe:

How to correctly bring the riser through the roof:

By correctly calculating the dimensions of the fan pipe and installing it in compliance with all installation rules, it is possible to completely eliminate the possibility of accumulation and the probability of sewer gases entering the house. And then there will definitely not be any problems with the operation of the sewer system.

Do you have practical skills in installing a ventilation fan pipe? Share your knowledge or ask questions on the topic - the communication block is located below.

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